The invention pertains to a method and a device for gathering printed sheets, particularly signatures and/or individual sheets.
During the gathering process in a book binding system, an individual signature is respectively withdrawn from several collections of identical signatures, wherein the various decollated signatures are delivered to a collecting conveyor in order to form stacks.
Known gathering machines feature feeder stations that are arranged in a row and respectively consist of a magazine for accommodating a signature stack, a withdrawal drum with a gripper mechanism for taking hold of and withdrawing the respective bottom signature that is tilted away from the signature stack, and an intermediate support for temporarily depositing the decollated signature. The collecting conveyor features a collecting channel that is oriented perpendicular to the signature withdrawal direction, wherein pushers of a transport chain moving in said collecting channel strip the decollated signatures off the individual intermediate supports and gather the signatures into a book block on the collecting channel.
Such a gathering machine that operates with a change of direction is described in DE 14 86 744 B. This machine furthermore features reciprocating intermediate tables for pre-accelerating the decollated signatures for the transport by the pushers of the collecting conveyor. Acceleration systems require further costly structural measures and also impair the functional reliability.
A gathering machine with feed stations according to the longitudinal withdrawal principle is known from DE 196 16 047 A1, wherein this gathering machine comprises a conveyor belt that carries a signature stack in a magazine such that a region of the folded edge remains exposed and respectively advances the bottom signature in a correspondingly cyclic fashion, as well as a withdrawal conveyor system that serves for receiving and additionally transporting the advanced signatures and is composed of acceleration rollers. A clamping conveyor consisting of an upper and a lower conveyor belt is arranged downstream of the withdrawal conveyor system and inclined toward the collecting conveyor, wherein this clamping conveyor deposits the decollated signatures on the stack being formed with a synchronous transport movement upstream of a pusher of the collecting conveyor. The signatures decollated by the feeder stations are delivered to the collecting conveyor without a change of direction.
Withdrawal systems operating in accordance with the longitudinal withdrawal principle are suitable for higher capacity ranges. However, since this frequently requires a labor-intensive replenishing of signatures in the magazines, bundle feeders that create a stream feed from the signatures stacked into (sheet) bundles are increasingly utilized for filling the magazines, wherein the signatures are quasi decollated. The stream feed is deposited in the form of a stack once again when the magazines are filled such that the signatures are decollated anew in the feeder stations. There also exist signature rolls with signatures that are wound up in a coil in a shingled arrangement. The stream feeds are unwound in unrolling stations and transferred into the magazines of the gathering machine. The regular arrangement of the signatures in the stream feed is lost when the magazines are filled such that the complex decollating process described above needs to be carried out.
US 2005 077 670 A1 describes a feeder station that consists of a bundle feeder and a transfer device, wherein the signatures decollated from the (sheet) bundle in the form of a stream feed are placed into a horizontal buffer station realized similar to a magazine in a waterfall-like fashion, and wherein the signatures are then withdrawn from the buffer station again in order to be perpendicularly delivered to the collecting conveyor by the transfer device. The thusly decollated signatures are ultimately deflected with a transfer device and delivered to the collecting conveyor. The signatures consequently are decollated twice in this case.
Decollating processes on stack magazines represent functionally critical process steps, particularly if a subsequent decollating process can only be initiated once the preceding signature is completely withdrawn from the magazine as is the case with the aforementioned feeder stations with transverse and longitudinal sheet withdrawal. Due to the parallel arrangement of several feeder stations on a gathering machine, a few malfunctions of individual feeder stations can already result in a substantial reduction of the net gathering capacity.
DE 33 15 489 A1 describes a method, in which a stream feed is divided into partial streams of signatures that are uniformly spaced apart from one another, wherein the partial streams are delivered to decollating devices, e.g., gripper drums, without magazining the signatures. The leading edges of the signatures lie on top of one another toward the front and need to reach the gripper drum synchronous with the gripping cycle. Another disadvantage can be seen in that the signatures are delivered into the collecting channel transverse to the collecting transport direction by the gripper drum such that a change of direction with correspondingly jerky transport movements takes place.